for the non computer-literate, let me explain (it won't be 100% precise for simplicity). say you have a process of some kind running on your computer (some program or whatever). and now some other process needs the cpu ( the computer's 'brain'). now the cpu is only able (on most computers) to do one thing at a time. so the other process interrupts the cpu. now if the interrupting process is higher-priority than the first process, it gets the cpu. so for example, if you're happily typing away at your keyboard doing some word processing, and your operating system needs to do some work in the background, it interrupts the charcter stream from your keyboard to the memory, so that you continue typing, but the characters stop appearing on the screen. this has probably happened to you. it is because operating-system processes are usually highr priority than most user actions. then, when the operating system is done, the cpu is free to continue helping you out, and then the characters start appearing on the screen again. now on to our story:

and their phone rings. you recognise the tune. a defilement of j.s. bach. a high priority interrupt to their cpu-for-a-brain. "hello?" they say. "oh hi....." you know the drill. and now people can see you walking down the street together. they are happily chatting away on their cell phone. you are trying to look like it's okay. you have loads of stuff to do while they're on the phone. oh look: there's a flower. that really is a lovely flower. lucky they're on the phone. you would have missed it.

now the thing about the cpu is this: it has a stack. it remembers where it left off. humans do not have a stack. humans have a short-term memory, a hippocampus, and other various memorabilia, in their head. not quite as effective as a stack.